Monohybrid Cross

A monohybrid cross is a genetic cross between two individuals that focuses on a single trait (or gene). Specifically, it examines the inheritance of one specific trait, which is typically determined by one gene with two different alleles (variants).

1. Trait Selection: Choose a specific trait to study. This trait should have two distinct phenotypic variants, often referred to as the dominant and recessive traits. For example, you could choose the trait of flower color in pea plants, where purple (P) is dominant and white (p) is recessive.

2.Parental Generation (P): Start with two purebred individuals, each exhibiting one of the two contrasting phenotypes for the chosen trait. In the case of flower color, you would have one purebred purple-flowered plant (PP) and one purebred white-flowered plant (pp).

3. Cross (F₁ Generation): Cross the two parental individuals by allowing them to breed. The offspring of this cross are called the first filial generation (F₁). In a monohybrid cross, all F₁ offspring will be heterozygous for the trait, having one dominant and one recessive allele (Pp).

4. Observations (F₁ Phenotype): Observe the phenotypes of the F₁ generation. In the case of the flower color trait, all F₁ plants will have purple flowers because the dominant allele (P) masks the expression of the recessive allele (p).

5. Cross (F₁ × F₁): Allow the F₁ individuals to cross-pollinate or self-fertilize, depending on the organism. The resulting offspring make up the second filial generation (F₂).

6. Observations (F₂ Phenotype): Observe the phenotypes of the F₂ generation. This is where the classic Mendelian ratios come into play. In a monohybrid cross, you will typically observe a phenotypic ratio of approximately 3:1. Three-quarters (75%) of the F₂ plants will exhibit the dominant phenotype, while one-quarter (25%) will exhibit the recessive phenotype.

The observed 3:1 ratio is a consequence of Mendel’s laws of inheritance, particularly the principles of dominant and recessive alleles, segregation, and independent assortment. It demonstrates how genetic information is passed from one generation to the next for a single trait.